Parallel Query has two components: a foreground process that acts as query coordinator and a set of parallel slaves (Pnnn) that are background processes. These background processes are spawned or reused during the start of a parallel statement. They receive and carry out units of work sent from the query coordinator.

The maximum number of Pnnn processes is controlled by the initialization parameter PARALLEL_MAX_SERVERS. Slave processes are numbered from 0 to the PARALLEL_MAX_SERVERS setting. If the query is a GV$ query, then these background processes are numbered backward, starting from PZ99.

It could be a bug if version matched in this document ( Bug 8656212 - Alert log with message "Warning: recovery process XXXX cannot use async I/O" (Doc ID 8656212.8) ) . Is this affect slow performance ? You can also open SR , but i think this messages are ignorable. And check below commands , async I/O enabled in your operating system.